Objectives: (a) To evaluate the serologic response to infection with B. pertussis and immunization with pertussis vaccine (b) To determine which serologic assays have the highest diagnostic sensitivity and specificity for pertussis and (c) To understand pertussis epidemiology in the community through seroprevalence and outbreak studies. (1) CDC Multicenter Surveillance Study: Evaluation of sera collected in this study has continuedby completing 3000 assays on approximately 750 sera. (2) Serodiagnosis: (a) Assays are in place to measure IgG, IgA, and IgM antibodies to PT, FHA, LOS, 69kDa protein, fimbriae, and whole bacteria. These 18 assays plus the whole-cell microagglutination assay have been performed on paired sera from 40 culture positive pertussis cases in order to document which assays have the highets diagnostic sensitivity. (b) Six different ELISA assays were performed on pared sera from 21 Swedish patients that has been serodiagnosed as pertussis by Dr. Marta Granstrom. LOP results confirmed those of Dr. Granstrom. (c) Four ELISA assays were performed on about 100 sera obtained from miscellaneous medical institutions in order to assist in the laboratory diagnosis. (3) Seroepidemiology: IgG and IgA anti-PT and FHA assays have been performed on about 400 sera obtained from foreign health officials. The purpose of the studies was to evaluate pertussis prevalence in the countries in order to assess the suitability of these sites for pertussis vaccine efficacy trials. (4) Response to infection and disease: The antibody response to the 69kDa protein in pertussis patients and whole-cell vaccinees was evaluated, and it was observed that over 80% of vaccinees and about 60% of patients respond to this protein.